The bass reproduction of audio signals in an electroacoustic converter, particularly a loudspeaker or an earpiece, is governed by the size of the electroacoustic converter (the loudspeaker of the earpiece). The smaller the loudspeaker membrane and its maximum deflection area, the higher the lower resonant frequency.
FIG. 1 shows a typical frequency curve of a small loudspeaker. Electronic audio devices, in which such small electroacoustic converters are used and in which the base reproduction is consequently unsatisfactory, are primarily audio devices (devices for output or reproduction of audio signals) of communication and information technology as well as entertainment and consumer electronics, such as mobile radio and cordless handsets, notebooks, Personal Digital Assistants, mini radios, radio alarm clocks, portable music players, etc.
To improve the bass reproduction with a small loudspeaker, a known psychoacoustic principle can be employed. This principle is called “Residual Hearing” (Hearing of Missing Fundamentals) or “Virtual Pitch.”
According to this principle, the perception of a basic frequency can be simulated by a combination of harmonic waves. Thus, the perception of a low frequency also can be simulated with the corresponding combination of its harmonic waves.
A more detailed description of the virtual pitch principle can be found in the publication “Psychoacoustics” by E. Zwicker; H. Fastl; Springer Verlag, 2nd. Edition, 1999.
Methods based on the psychoacoustic principle are known from U.S. Pat. Nos. 6,111,960 and 5,930,373, which use the audio signal to generate a corresponding series of harmonic waves to simulate the frequencies below the limit frequency.
From WO 00/15003, a method based on the psychoacoustic principle is known in which the harmonic waves present in the audio signal are amplified. In this case, to improve the bass reproduction of the audio signal, low-frequency components of the audio signal are isolated in electroacoustic converters into a low-frequency audio signal, the isolated low frequency components filtered with a number of bandpass filters, the bandpass-filtered frequency components amplified in an amplifier that can be controlled with regard to the gain factor, in which case the gain factor is obtained from the envelopes of the bandpass filtered frequency components, and a simulated low frequency audio signal is created by combining the original audio signal with the amplified frequency components.
An object of the present invention is to control the bass reproduction of audio signals in an electroacoustic converter based on the virtual pitch or residual hearing psychoacoustic principle in such a way that the perception of the virtual bass reproduction of the audio signals is improved compared to the prior art